Warm-weather rashes.

Summertime is here, but dermatologists are warning that the warm weather brings out some very common rashes:

Swimmer's itch. The bacteria and other organisms that thrive in many lakes and swimming areas can cause little bumps on the arms, legs, chest, or bottom. This may be a reaction to too much contact with water, whether sitting around in a wet bathing suit or staying too long in a hot tub.

Dermatologists recommend a shower with soap and water after swimming and an application of calamine lotion on the rash. Keep skin as dry as possible and stay out of the water for a few days to give the rash some time to heal. If the itching doesn't stop, an over-the-counter hydrocortisone cream every four hours is recommended. Try a diaper rash ointment if the skin feels sore rather than itchy.

Prickly heat. Babies get this, but adults can too if the weather's hot and humid. The medical name for this problem is miliaria. The tiny little red bumps of prickly heat are found on skin Folds. To ease this problem, keep cool and dry and wear clothing made of natural fibers such as co,on or linen. Avoid tight-fitting garments that trap moisture, especially those made of rubber or polyester. Pat dry thoroughly after bathing and dust on a cornstarch-based body powder before dressing.

Poison ivy. The sticky substance contained in poison ivy, oak, and sumac plants can adhere to clothing, garden tools, lawn furniture, or pets. If exposed to it, immediately wash the affected areas with cold running water and soap if available. Any affected clothing should be washed or dry-cleaned. Rinse off all equipment before bringing it indoors, since running water neutralizes the sticky sap and prevents it from spreading.

Hives from the heat. Hot weather, vigorous exercise, or stress are among the causes of hives. Intense itching is rapidly followed by the appearance of raised skin bumps and large patches of reddened skin around them. This intense reaction can last up to four hours and take one or two days to calm down. Physicians can prescribe antihistamines for relief, but the best way to prevent an outbreak is to avoid what triggers it. Hives can also result from chiggers, which are tiny red bugs called harvest mites. While they only bite and don't burrow into the skin, they can cause redness, itching, and rash. Use mosquito repellent to prevent this,but if bitten, shower or bathe as soon as possible and use calamine lotion to relieve the irritation.

Impetigo. This skin rash has a characteristic honey-yellow color as it crusts over. Impetigo is the number one rash among children and will spread rapidly in warm weather. The cause is usually bacteria called Staphylococcus aureus. This infection responds to prescription medication.

Ticks, scabies, and other bugs. Hikers and campers should be reminded that the deer tick, which may carry the germ for Lyme disease, is identified by a distinctive, circular red marking on the skin around the bite. Ticks can also transmit Rocky Mountain spotted fever and tularemia, a disease that causes fever, chills, and headache. If exposed to tick-borne disease, consult a physician immediately.

Scabies, a condition caused by an itch mite that burrows into skin and lays its eggs between warm, moist skin folds, is very common. The danger from scabies is that bacterial infections may develop through skin openings as a result of vigorous scratching. A dermatologist can prescribe a suitable cream or lotion to get rid of the mites and their eggs.

Contact dermatitis from the environment. An on-the-ob rash can develop simply because workers wearless clothing in the heat and expose more of their skin to irritating substances. A virtually endless list of common substances from metals, chemicals, and solvents to plants and insecticides can cause skin to overreact with a rash. The only solution is to protect skin as much as conditions allow. Once the skin becomes sensitized to a substance, it will always react in the future.

Polymorphic light eruption, or PLE. PLE is a skin rash that develops as a result of an allergic reaction to certain wavelengths of sunlight. Corticosteroid creams can be prescribed to relieve the symptoms. Those who develop this condition need to be especially vigilant about the use of protective sunscreen. Dermatologists recommend a minimum SPF (sun protection factor)of 15 or greater.

Acne mechanica. An existing tendency to acne can be accentuated in the heat by anything that rubs against the face, shoulders, or back.

Even many hours with a telephone pressed against the cheek, or resting chin on hands, can have similar results. Contrary to popular belief, excessive scrubbing with abrasives or harsh cleansers doesn't help acne, and does irritate skin.

Diaper rash. Infants with diaper rash should have their diapers changed more Frequently. The longer a baby's skin remains in contact with body wastes, the more likely it is to become irritated or damaged, since bacteria and yeast thrive in warm, moist environments. Cleanse baby's skin with every change, and wipe dry gently. Diaper ointments are useful,but if a diaper rash doesn't improve, allow the infant to go diaperless whenever possible. If the rash still doesn't improve, see a physician about antibacterial medication.

American Academy of Dermatology, P.O. Box 1661, Evanston, Illinois 60204-1661.